1. Field of the Invention
The present invention relates to an apparatus and method for recompleting a well and, more particularly, to recompleting a well using coiled tubing.
2. Description of Related Art
Once an oil or gas well has been drilled, the oil or gas is generally produced from the well by introducing into the borehole well tubing which is of smaller diameter than the borehole, together with associated production equipment to deliver the oil or gas upwardly through the well tubing to the surface. The well tubing normally comprises interconnected rigid threaded sections of pipe hung from a tubing hanger positioned at the upper end of the borehole.
In the course of production, however, it may happen that it becomes no longer possible to continue production from the well with the existing apparatus. This may be due, for example, to failure in some part of the production equipment or it may happen that the downhole pressure may fall to an extent whereby it becomes impossible to deliver the oil or gas upwardly through the existing well tubing.
In the past such failure of production made it necessary to kill the well and to remove, and repair or replace, the entire production installation, which was a lengthy and costly operation and which could also result in damage to the well. It has therefore been proposed, for example as described in U.S. Pat. No. 4,844,166, to recomplete a failed well by passing coiled tubing down through the primary well tubing, together with the equipment and accessories necessary for allowing oil or gas to continue to be delivered to the surface through the coiled tubing.
Coiled tubing is a continuous flexible pipe wound on a reel and which can be unreeled as it is passed down the borehole. The tubing is normally of small diameter compared to normal production well tubing, and may have a diameter of only 1-11/2 inches. The advantage of using coiled tubing for well recompletion is that it does not require the well to be killed and also avoids the costly removal and replacement of the primary well tubing and associated production equipment.
However, as previously mentioned, the primary production tubing for a well is normally supported at the upper end of the well by a tubing hanger, and where coiled tubing is subsequently employed for recompletion the coiled tubing also requires to be supported in similar fashion. In addition, the arrangement for supporting the coiled tubing may require to permit communication to subsurface equipment, such as a subsurface safety valve. At present coiled tubing completions which require communication to subsurface equipment must be hung off in a modified tubing hanger. However, modifying the existing tubing hanger to support the coiled tubing in a manner to provide communication to subsurface equipment is currently an expensive operation, and there is therefore a requirement for a simpler and less expensive system for supporting the coiled tubing completion assembly.